Process for reducing the processing time in the production of polyesters

ABSTRACT

Polyesters obtained by reacting isophthalic acid or terephthalic acid with a polyol with or without a catalyst in a first stage to form a half-ester mixture which is reacted in a second stage with an aliphatic polycarboxylic acid are produced at reduced processing times. In the first stage a portion of the total polyol to be reacted is contacted with substantially all of the isophthalic acid or terephthalic acid. Then, this mixture is heated with agitation to a temperature of at least 190° C. and the remaining portion of the polyol is added to the heated mixture with agitation in such a manner that the temperature remains at or above the 190° C. This temperature is maintained until the reaction to form a half-ester mixture is completed. This reaction may be conducted in the presence of an esterification catalyst. The polyester-monomer mixture is reacted in a second stage with an aliphatic polycarboxylic acid to produce the polyester.

BACKGROUND OF THE INVENTION

This invention relates to a process for the production of polyestersfrom isophthalic acid or terephthalic acid. In particular, thisinvention relates to a process for the production of unsaturatedpolyesters from isophthalic acid or terephthalic acid, a polyol and anunsaturated aliphatic polycarboxylic acid.

When isophthalic acid and terephthalic acid were substituted forphthalic anhydride in the production of polyesters, the one-stageprocess used with phthalic anhydride was not as effective. The artdeveloped a two-stage process in which polyesters were produced fromisophthalic acid or terephthalic acid, a polyhydric alcohol, or polyol,and a saturated or unsaturated polycarboxylic acid.

One two-stage process is disclosed in U.S. Pat. No. 2,904,533 (Carlsonet al). In the first stage the isophthalic acid is polycondensed withall of the glycol until essentially a zero acid number product mixtureis obtained. Then, this product mixture has an unsaturated acid, such asmaleic acid or anhydride, added to it until the desired acid number andunsaturated polyester is obtained. This two-stage process wassubsequently improved by conducting the first stage reaction so most butnot all of the water of esterification that theoretically could beproduced was removed .[.for.]. .Iadd.from .Iaddend.the first stage.Another improvement .[.on.]. .Iadd.in .Iaddend.this two-stage process isthe use of two dihydric alcohols of different carbon atom content. Thisprocess is disclosed in U.S. Pat. No. 3,196,131 (Mayer et al.). Thehigher boiling alcohol is charged to the first stage along with thearomatic dicarboxylic acid such as isophthalic acid. The unsaturatedacid, the other dihydric alcohol and remaining first alcohol, if any,are charged to the second stage.

Another two-stage process is disclosed in U.S. Pat. No. 3,345,339(Parker et al.). In the first stage a part of the polyol ingredient isreacted with isophthalic acid or terephthalic acid in the presence of anesterification catalyst, a tin compound, and in the substantial absenceof an alpha, beta-ethylenically unsaturated polycarboxylic acid. In thesecond stage an alpha, beta-ethylenically unsaturated polycarboxylicacid is reacted with the reaction product mixture of the first stage.

All of these two-stage processes endeavor to increase the effectivenessof using isophthalic acid or terephthalic acid from that of a one-stepprocess. In the two-stage process there is a serious disability over theone-stage process. The two-stage process takes from two to three timesthe number of hours to complete a polyester preparation as does theone-stage process. The above discussed patents purport to overcome thisdisadvantage in duration of processing time. The reduction in theduration of processing time effected by the two-stage process used inthe prior art can be improved.

The object of this invention is to provide a process that reduces theprocessing time in the production of a polyester in a two-stage processfrom isophthalic acid or terephthalic acid, a polyol and a saturated orunsaturated aliphatic polycarboxylic acid.

SUMMARY OF THE INVENTION

The present invention is an improvement in the first stagepolycondensation reaction of a two-stage process for the production of apolyester from isophthalic acid or terephthalic acid, a polyol, and asaturated or unsaturated aliphatic polycarboxylic acid. The isophthalicor terephthalic acid is reacted with at least a theoretical amount ofpolyol in the first stage to form a half-ester mixture of isophthalic orterephthalic acid and polyol. This mixture is reacted with the saturatedor unsaturated aliphatic polycarboxylic acid in the second stage to formthe polyester. The theoretical amount of polyol introduced in the firststage is approximately one equivalent of polyol for each equivalent ofacid needed to produce the polyester.

The improvement embodying the present invention is to decrease theinitial portion of polyol reacted with the isophthalic or terephthalicacid and heat this mixture to a temperature of at least 190° C., andthen add the remaining portion of the polyol to this heated mixture atsuch a rate that the temperature does not drop below the 190° C.

The improvement in such a first stage esterification comprises:contacting a portion of the total amount of polyol with substantiallyall of the isophthalic or terephthalic acid wherein said portion issufficient to make an agitatable mixture with the isophthalic orterephthalic acid, heating the agitatable mixture with agitation to atemperature of at least 190° C. where the reaction of isophthalic orterephthalic acid with polyol to form a half-ester mixture proceeds at asatisfactory rate, and adding the remaining portion of the total amountof polyol to the heated agitatable mixture in such a manner that thetemperature of the heated agitatable mixture remains at or above 190° C.whereby a half-ester mixture is obtained.

An esterification catalyst or initiator may be added to the first stageesterification reaction in order to reduce further the duration ofprocessing time of the polyester. Generally, the catalyst can be anytin, lead or lithium catalyst or initiator or any other catalyst orinitiator known in the art to catalyze or initiate the reaction ofisophthalic acid terephthalic acid and polyols. The reaction of theremaining portion of polyol with the agitatable mixture may beaccomplished by adding the remaining portion continuously orincrementally. Also, the remaining portion of polyol may be heated andadded to the heated agitatable mixture.

All the isophthalic or terephthalic acid need not be contacted initiallywith the first portion of the total amount of polyol. A substantialamount of the isophthalic or terephthalic acid should be contactedinitially and the remaining amount of the isophthalic or terephthalicacid should be contacted before the remaining portion of the totalamount of polyol is added to the heated agitatable mixture which alreadycontains an amount of the half-ester.

The agitatable mixture is heated at ambient pressure to at least atemperature of 190° C. and maintained at least at this temperature whilethe remaining portion of polyol is added. However, the temperature canbe as much above 190° C. as the esterification equipment will allow butthe polyester resin produced may have undesired characteristics if thetemperature is too high. Therefore, the temperature should not be above230° C. If a pressure other than ambient pressure is used thetemperature should still be at least 190° C.

The term "polyester" describes the di-ester polymer product wherein bothof the carboxylic acid groups of the diacid of isophthalic acid orterephthalic acid have reacted to form a polymer.

The term "half-ester mixture" describes the mixture obtained from thereaction between the isophthalic acid or terephthalic acid and thepolyol. This mixture consists mainly of the mono-ester wherein only oneof the carboxylic acid groups of the diacid of isophthalic acid orterephthalic acid have reacted with the polyol. The mixture may alsocontain a trace amount of diacid product between isophthalic orterephthalic acid and polyol, i.e., poly-di-ester, and other furtherreacted compounds.

The term "total amount of polyol" means an amount of polyol in a rangefrom at least the theoretical amount, which is one equivalent of polyolfor each equivalent of acid to produce the polyester, up to an amountusually not more than 125 percent of the theoretical amount. More of anexcess may be used but it would lessen the effectiveness of the process.

The term "agitatable mixture" means a mixture between substantially allof the isophthalic acid or terephthalic acid and the first portion ofpolyol which is in an amount to allow mixing in conventional mixingequipment used in the production of polyesters from isophthalic orterephthalic acid. The agitatable mixture of isophthalic or terephthalicacid and first portion of the total amount of polyol must be mixed inorder to provide even temperatures throughout the mixture.

The term "acid" as used in the discussion of the process of thisinvention and in the appended claims includes the correspondinganhydrides where such anhydrides exist.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the remaining discussion of the process of this invention theterm "isophthalic acid" shall include the term "terephthalic acid"unless otherwise expressly stated.

A problem in reducing the processing time in a two-stage process for theproduction of a polyester from isophthalic acid, at least a theoreticalamount of polyol, and a saturated or unsaturated aliphaticpolycarboxylic acid or anhydride is the first stage reaction rate. Thisesterification reaction rate is very slow until an adequate temperatureis obtained. Broadly, a temperature of at least 190° C. but preferably195° C. is the temperature around which the reaction should beconducted. The desired reaction temperature in the range of 190°-230° C.and preferably in the range of 195°-210° C. appears to be limited by theboiling point of the reaction mixture when all of the total amount ofpolyol is contacted at once with all of the isophthalic acid. A reactionmixture of a portion of the total amount of polyol and isophthalic acidachieves the desired reaction temperature more quickly.

The total amount of polyol is commonly in the range of about 105 to 110percent of the theoretical amount needed. The first portion of the totalamount of polyol is at least an amount that makes a substantial amountof the isophthalic acid mixable or agitatable with the liquid polyol.The amount of polyol in the first portion should not exceed an amountslightly less than the theoretical amount of polyol needed to react withthe isophthalic acid and saturated or unsaturated aliphaticpolycarboxylic acid to form the polyester. The closer the first portioncomes to this theoretical amount, the smaller the amount of reduction inprocessing time. The amount of polyol in the first portion of polyol isin the range of 0.5 to 1.7 moles per mole of isophthalic acid andpreferably in the range of 0.8-1.4 moles per mole of isophthalic acid.Also a solvent can be used to make the isophthalic acid more soluble inthe polyol. If a solvent is used, it is preferably a non-reactivesolvent which forms an azeotrope with water. Typical of such a solventis xylene.

The amount of isophthalic acid with which the first portion of polyol iscontacted need not be all the isophthalic acid that is going to bereacted. The amount of isophthalic acid need be only a substantialamount of the total amount of isophthalic acid to be reacted. Thissubstantial amount is that amount which will form an agitatable mixtureof isophthalic acid and polyol with the use of amounts of polyol thatare less .[.that.]. .Iadd.than .Iaddend.the theoretical amount. Thisamount is in the range of 50 to 90 percent by weight of the total amountof isophthalic acid to be used, which depends on the formulation for theparticular polyester desired.

The agitatable mixture of isophthalic acid and .Iadd.the .Iaddend.firstportion of polyol is heated while being agitated to a temperature whichis at least a temperature of 190° C. and is preferably in the range of195°-210° C. While the agitatable reaction mixture is at thistemperature, the remaining portion of the total amount of polyol isadded to the mixture in such a manner as not to reduce the temperaturebelow the temperature of 190° C. and preferably 195° C. This manner maybe performed by adding the remaining portion of polyol at such a ratethat the temperature is not decreased. The rate of addition may beaccelerated by heating the remaining portion of polyol before it isadded to the heated agitatable mixture to a temperature above ambienttemperature but below the boiling temperature of the polyol. Thisagitatable reaction mixture containing the total amount of polyolcontinues to react to produce a half-ester mixture. The esterificationreaction was taking place since the first portion of polyol wascontacted with isophthalic acid and the resulting agitatable mixture washeated to the adequate reaction temperature of at least 190° C. Theesterification reaction continues until the reaction is complete asindicated by the acid number of the half-ester mixture. If the finaldesired acid number of the half-ester mixture is reached before all ofthe remaining portion of polyol is added, the excess polyol that is leftmay be used as a coolant. The coolant would aid in cooling thehalf-ester mixture before the addition of aliphatic polycarboxylic acid.The half-ester mixture produced is composed of isophthalic acid andpolyol and has an acid number of less than 90 milligrams of potassiumhydroxide to neutralize 1 gram of the half-ester mixture.

This half-ester mixture is reacted with an aliphatic polycarboxylic acidin the second stage. The aliphatic polycarboxylic acid may be saturatedor unsaturated but is preferably unsaturated. This second stage isconducted in any manner known to those skilled in the art of two-stagepolyester production processes. The product from the second stage is thepolyester having a desired acid number.

The polyester produced by the improved process of this invention can beprepared from those polyols or a mixture of those polyols utilized inconventional processes. These polyols include: ethylene glycol,propylene glycol, butylene glycol, diethylene glycol, dipropyleneglycol, triethylene glycol, neopentyl glycol, trimethylene glycol,polyethylene glycol, polypropylene glycol, 1,6-hexanediol,1,5-pentanediol, trimethylolethane, trimethylolpropane, glycerol,1,2,6-hexanetriol, pentaerythritol, sorbitol, mannitol, methylglycoside, and the like. Other polyols including unsaturated polyols maybe used alone or in addition to the above mentioned polyols. This listof polyols is exemplary of the polyol that may be used, and the list isnot exhaustive. Typically, the total amount of polyol up to 125% oftheoretical is used but even greater excesses may be utilized ifdesired.

The aliphatic polycarboxylic acid used in the production of thepolyester by the improved process of this invention may be any of thepolycarboxylic acids conventionally used. Examples of suchpolycarboxylic acids include: maleic acid, fumaric acid, itaconic acid,citraconic acid, glutaconic acid, mesaconic acid. Other polycarboxylicacids including saturated polycarboxylic acids may be used in additionto the above-mentioned acids.

The polyester may be produced by the process of this invention with evena greater reduction in processing time when an esterification catalystor mixture of esterification catalyst is used in the first stage.Catalysts known by those skilled in the art to be effective in theesterification reaction of the first stage include inorganic salts andorganic compounds of tin, lead or lithium. Examples of inorganic tinsalts include: stannous salts, such as stannous halides, like stannousbromide, stannous chloride, stannous fluoride, stannous iodide, stannousoxychloride; and other stannous salts, like stannous hydroxide, stannoussulfate, stannous oxide, stannous acetate; and stannic salts, such asstannic chloride, stannic bromide, stannic fluoride, and stannicoxychloride; and stannous acylates; and stannous alkoxides. Examples oforganic tin compounds include dialkyltin salts of carboxylic acid, likedibutyltin diacetate, dibutyltin dilurate and dibutyltin maleate; anddialkyltin chlorides, like dibutyltin chloride; and dialkyltin oxides,like dibutyltin oxide, and dilaryltin oxide; and trialkyltin hydroxides,like tributyltin hydroxide and trimethyltin hydroxide. These catalystsare effective in amounts of about 0.01 percent by weight to about 2.0percent by weight of the total weight of the charge in the first stage.Higher quantities of catalysts can be used if desired. Other catalystsknown to those skilled in the art that may be used in the improvedprocess of this invention are tetrabutyl zirconium and zirconiumnaphthonate.

In the preferred embodiment of the process of this invention isophthalicacid and not terephthalic acid is used as the aromatic polycarboxylicacid to be esterified. Propylene glycol is the preferred polyol used inthe improved process of this invention. The total amount of propyleneglycol is a theoretical amount of around 2 moles of propylene glycol permole of isophthalic acid and maleic acid. The preferred catalyst isdibutyltin oxide in an amount of around 0.2 percent by weight of totalweight charged to the first stage. The production of the polyester isconducted in the presence of an inert gas at atmospheric pressure.

All of the isophthalic acid is added to a suitable reaction vessel forcarrying out condensation reactions. This vessel may be constructed ofstainless steel or it may be a glass-lined kettle which is insulated toprevent heat loss. The vessel should be equipped with an agitator,heating and cooling coils, a temperature measuring device, vapor removalequipment for continuous removal of water of esterification, and mayinclude vapor columns designed to minimize loss of low boiling polyols.The vessel also contains an inert gas inlet for conducting the reactionin an inert atmosphere of nitrogen. The first portion of total amount ofpropylene glycol is added to this vessel which contains all theisophthalic acid to be reacted. The amount of propylene glycol in thisfirst portion is in the range of 0.8-1.4 moles per mole of isophthalicacid but most preferably in the range of 0.9-1.0 mole per mole ofisophthalic acid. The resulting mixture is quite thick but it can beagitated and it becomes more fluid when the temperature is increased.

This resulting agitatable mixture of isophthalic acid and first portionof propylene glycol is agitated and heated to a temperature of at least190° C. and preferably in the range of 195° C.-210° C. at ambientpressure. This temperature is quickly and easily obtained. When thetemperature reaches about 198° C., the remaining portion of the totalamount of propylene glycol is added to the mixture of isophthalic acidand first portion of propylene glycol. This addition is at the fastestpractical rate while maintaining a minimum temperature of at least 190°C. and preferably 195° C. Upon completion of the addition of theremaining portion of propylene glycol, the first stage reaction iscontinued to completion which is indicated by the acid number of theproduct. The product of the first stage is a half-ester mixture ofisophthalic acid and propylene glycol which has an acid number of lessthan 90 milligrams and preferably in the range of 20-90 milligrams ofpotassium hydroxide to neutralize 1 gram of half-ester mixture.

The vessel containing the half-ester mixture is cooled to around 150° C.and maleic anhydride is added. The maleic anhydride is the preferredaliphatic polycarboxylic acid. The vessel is heated to a temperature ofaround 200° C. and held at this temperature for the duration of thepolyesterification reaction. The duration depends on the desired acidnumber in the final product. After the desired acid number is obtained,the reactor is cooled. The product from the second stage is theunsaturated polyester.

The unsaturated polyesters produced by the improved process of thisinvention can be thinned in a suitable reactive monomer in a mannerknown to those skilled in the art.

For a better understanding of the invention reference should be had tothe following examples. In the following examples the term isophthalicacid does not include the term terephthalic acid.

ILLUSTRATIVE EXAMPLE NO. 1

For the purposes of comparison unsaturated polyester was prepared fromisophthalic acid, propylene glycol and maleic anhydride according to aconventional two-stage process. All of the propylene glycol, which was atheoretical amount of the two moles of propylene glycol to one mole ofisophthalic acid considering the one mole of maleic anhydride to beadded to form the polyester, was added to the isophthalic acid. A weightpercent amount of 36.5% of propylene glycol was added to 39.9 wt. % ofisophthalic acid, based on a total weight of the components, for thefinal unsaturated polyester. This mixture was heated to the adequatereaction temperature of 200° C. and held until the acid number of thehalf-ester mixture produced decreased to 25-30 milligrams. The mixturewas cooled and 23.6 wt. % of maleic anhydride was added to produce theunsaturated polyester. The yield was 96.7% of the theoretical yield. Thefirst stage processing time was 111/4 hours.

EXAMPLE NO. 2

A first portion of 7,310 kg of propylene glycol was added to 11,402 kgof isophthalic acid. This gave a mixture having a 1.4/1.0 moler ratio ofpropylene glycol to isophthalic acid. This mixture was agitated andheated to 198° C. The remaining portion of propylene glycol, 3,132 kgequivalent to 0.6 moles per mole of isophthalic acid, was added to theheated agitatable mixture in 23/4 hours, thus, holding the reactiontemperature at 198° C. The reaction was continued until the half-estermixture had an acid number of 25 to 30 milligrams at 200° C. without theuse of a catalyst. The half-ester mixture which contained theesterification product of propylene glycol and isophthalic acid wascooled. Then maleic anhydride in an amount of 6,732 kg was added. Thiscombination of half-ester mixture and maleic anhydride was heated to atemperature of around 200° C. This temperature is maintained until thedesired acid number of the unsaturated polyester was achieved. Then thetemperature was decreased and the product, an unsaturated polyesterresin, was removed. The first stage processing time was 71/2 hours. Thisis a processing time savings of 40% compared to the conventional processin Illustrative Example No. 1.

EXAMPLE NO. 3

A first portion of propylene glycol equaling 4,614 kg was added to 7,279kg of isophthalic acid. The resulting mixture had a moler ratio of1.4/1.0 propylene glycol to isophthalic acid. An amount of dibutyl tinoxide of 57 kg or 0.2 wt. %, based on the total weight of components inthe charge to the first stage, was added to the mixture. The mixture wasagitated and heated to 185° C. at which temperature the mixture becamemore fluid. An additional amount of 3,919 kg of isophthalic acid wasadded to the mixture. This addition brought the moler ratio of propyleneglycol to isophthalic acid to 0.9/1.0 in the mixture. The mixture wasagitated and heated to 198° C. and the balance of the propylene glycol,6,152 kg (1.20 moles/mole of isophthalic acid), was added in 2-3/4 hoursthus maintaining the reaction temperature at 198° C. This addition ofthe balance of the propylene glycol was at such a rate that thetemperature of the reaction did not decrease below 198° C. This additionconsisted of dribbling the remaining portion of the propylene glycolinto the heated, agitated mixture from a weigh tank.

After the addition of all of the balance of propylene glycol the mixturewas held at 200° C. until the acid number decreased to 25 to 30milligrams and the half-ester mixture was cooled to a temperature ofaround 150° C. Maleic anhydride in an amount of 6,732 kg was added andthe combination of half-ester mixture and maleic anhydride was heated toa temperature of around 200° C. The temperature is held until thedesired acid number product is obtained. Then the reactor vessel wascooled and the unsaturated polyester removed. The first stage processingtime was 71/2 hours.

Table I summarizes the first stage processing time results of severalruns conducted by the two-step glycol addition of the improved processof this invention and a conventional two-stage process. The conventionaltwo-stage process runs are for the purpose of comparison. Theconventional runs were conducted in a similar manner as IllustrativeExample No. 1 and a few of the conventional runs were performed with adibutyl tin oxide catalyst. The runs according to the improved processof this invention were conducted in a manner similar to Example No. 2with and without the use of a catalyst. The results indicated that theimproved process of this invention, even without the use of a catalyst,improves the processing time of a two-step process better than the useof a catalyst in a conventional two-step process.

                  TABLE I                                                         ______________________________________                                        Processing Time Comparison                                                                         % Wt.     Processing Time                                Run #    Process Used                                                                              DBTO*     1st Stage,Hrs.                                 ______________________________________                                        1        Conventional                                                                              None      12                                             2        Conventional                                                                              None      11                                             3        Conventional                                                                              None      9                                              4        Conventional                                                                              None      9                                              5        2-Step Glycol                                                                             None      71/2                                                    Addition                                                             6        Conventional                                                                              0.1       10                                             7        2-Step Glycol                                                                             0.1       6                                                       Addition                                                             8        Conventional                                                                              0.2       10                                             9        2-Step Glycol                                                                             0.2       4                                                       Addition                                                             10       2-Step Glycol                                                                             0.2       4                                                       Addition                                                             ______________________________________                                         *Dibutyltin oxide                                                        

According to the provisions of the patent statutes, I have explained theprinciple, preferred construction and mode of operation of my inventionand have illustrated and described what I now consider to represent itsbest embodiment. However, I desire to have it understood that within thescope of the appended claims, the invention may be practiced otherwisethan as specifically illustrated and described.

I claim:
 1. In a two-stage process for the production of polyesterswherein an aromatic polycarboxylic acid selected from the groupconsisting of isophthalic acid and terephthalic acid is reacted in thefirst stage with a polyol to produce half-ester mixture which is reactedwith a saturated or unsaturated aliphatic polycarboxylic in the secondstage to produce the polyester, to reduce the processing time in thefirst stage; thereby reducing the processing time for the production ofthe polyester, comprising:a. contacting first portion of the polyol withthe aromatic polycarboxylic acid in the first stage in an amount atleast sufficient to form an agitatable mixture with the aromaticpolycarboxylic acid but in an amount slightly less than the theoreticalamount of polyol needed to react with the isophthalic acid orterephthalic acid and saturated or unsaturated aliphatic polycarboxylicacid, b. heating the agitatable mixture .Iadd.with agitation .Iaddend.toa temperature of at least 190° C. to 230° C., and c. adding theremaining portion of the polyol to the heated agitatable mixture.Iadd.with agitation .Iaddend.in the first stage in such a manner thatthe temperature of the heated agitatable mixture is maintained at atemperature of at least 190° C. in order to produce a half-estermixture.
 2. A process according to claim 1 wherein an esterificationcatalyst selected from the group consisting of inorganic salts andorganic compounds of tin, lead or lithium and mixtures of said salts andcompounds, and tetrabutyl zirconate, and zirconium naphthenate is usedin the first stage during contacting of the first portion of polyol andaromatic polycarboxylic acid and heating of the agitatable mixture andadding the remaining portion of polyol to the heated agitatable mixture.3. A process according to claim 2 wherein the catalyst is dibutyl tinoxide present in an amount of 0.01 to 2.0 percent by weight of the totalweight of the charge in the first stage.
 4. A process according to claim1 wherein the unsaturated polycarboxylic acid is selected from the groupof acids and anhydrides consisting of maleic acid or anhydride, fumaricacid or anhydride, itaconic acid or anhydride, citraconic acid oranhydride, glutaconic acid or anhydride, and mesaconic acid oranhydride.
 5. A process according to claim 1 wherein the polyol isselected from the group consisting of ethylene glycol, propylene glycol,butylene glycol, diethylene glycol, dipropylene glycol, triethyleneglycol, neopentyl glycol, trimethylene glycol, polyethylene glycol andpolypropylene glycol.
 6. A process according to claim 1 wherein theamount of polyol present in the first portion of polyol is in the rangeof 0.5 to 1.7 moles of polyol per mole of aromatic polycarboxylic acid.7. A process according to claim 1 wherein the remaining portion ofpolyol is heated to a temperature in the range from ambient temperatureto a temperature less than the boiling point of the polyol before theremaining portion is added to the heated agitatable mixture in order toadd the remaining portion of polyol while maintaining the temperature ofthe heated agitatable mixture at a temperature of at least 190° C.
 8. Aprocess according to claim 1 wherein the first portion of polyol iscontacted with a first portion of the aromatic polycarboxylic acidpresent in a substantial amount and the remaining portion of thearomatic polycarboxylic acid is added after the mixture of the firstportions of polyol and aromatic polycarboxylic acid is heated. l
 9. Aprocess according to claim 1 wherein the amount of polyol present in thefirst portion of polyol is in the range of 0.8 to 1.4 moles of polyolper mole of aromatic polycarboxylic acid.